(1) Field of the Invention
The present invention relates to a process and apparatus for the preparation of a semiconductor device. More particularly, the present invention relates to a process and apparatus for recrystallizing polycrystalline or amorphous silicon.
(2) Description of the Related Art
In the semiconductor industry, a three-dimensional structure has attracted attention as a means of increasing the degree of integration and the operating speed, and as a means of realizing this structure, there has been proposed an SOI (semiconductor-on-insulator) technique of forming a recrystallized silicon layer capable of forming an element thereon on an insulating film.
In this SOI technique, the recrystallized silicon is formed by melting and recrystallizing polycrystalline silicon deposited on an insulating film by energy beams, but often the melted silicon is peeled from the insulating film. Accordingly, the development of a process for eliminating this defect is desired.
When a substrate having an SOI structure, which is used for a three-dimensional IC or the like, is prepared, an interlaminar insulating film, for example, silicon dioxide (SiO.sub.2), is formed on a silicon (Si) substrate having semiconductor elements formed thereon, a polycrystalline Si layer is deposited on this SiO.sub.2 film by the chemical vapor deposition (CVD) method, and energy beams, for example, laser beams, are vertically scanned over the polycrystalline Si layer so that the end portions of the beam-irradiated regions are overlapped, whereby the polycrystalline silicon is melted and recrystallized in sequence and a recrystallized Si layer having a single crystal region covering a broad area sufficient to form semiconductor elements thereon is formed on the SiO.sub.2 film.
In the conventional technique, the incident angle of the laser beams having a predetermined beam spot diameter to the substrate is fixed, and scanning is carried out in sequence at a predetermined constant speed.
In the conventional beam annealing method and apparatus where the polycrystalline Si layer is melted and converted to a single crystal in sequence, where the recrystallization is carried out under the conditions of an efficient melting of the polycrystalline Si and giving an efficient treatment, for example, a power density of 10.sup.6 to 10.sup.7 W/cm.sup.2 and a scanning speed of about 2 to about 3 mm/sec, a peeling of the melted Si from the surface of the SiO.sub.2 film often occurs, whereby holes exposing the SiO.sub.2 film are formed in the Si surface at a high density and only a recrystallized Si layer that cannot be practically used is formed.
According to the conventional technique, this peeling is controlled by reducing the beam intensity, i.e., the power density of laser beams, but this conventional method is defective in that the melting width is narrowed by a reduction of the power density, with the result that the crystal quality is lowered and the treatment time is greatly prolonged.